[Bug rust/107633] New: [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[Bug rust/107633] New: [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[ro at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

            Bug ID: 107633
           Summary: [13 regression] Bootstrap failure due to
                    -Werror=unused-parameter and
                    -Werror=dangling-reference
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rust
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ro at gcc dot gnu.org
                CC: dkm at gcc dot gnu.org
  Target Milestone: ---
              Host: i386-pc-solaris2.11
            Target: i386-pc-solaris2.11
             Build: i386-pc-solaris2.11

I just tried bootstrapping the current devel/rust/master branch on Solaris/x86,
but ran into quite number of failues:

* For one, there were hundreds of instances of -Werror=unused-parameter, e.g.

/vol/gcc/src/hg/master/rust/gcc/rust/lex/rust-lex.cc: In member function
'std::tuple<Rust::Codepoint, int, bool> Rust::Lexer::parse_utf8_escape(char)':
/vol/gcc/src/hg/master/rust/gcc/rust/lex/rust-lex.cc:1326:32: error: unused
parameter 'opening_char' [-Werror=unused-parameter]
 1326 | Lexer::parse_utf8_escape (char opening_char)
      |                           ~~~~~^~~~~~~~~~~~
/vol/gcc/src/hg/master/rust/gcc/rust/ast/rust-ast-dump.cc: In member function
'virtual void Rust::AST::Dump::visit(Rust::AST::AttrInputMetaItemContainer&)':
/vol/gcc/src/hg/master/rust/gcc/rust/ast/rust-ast-dump.cc:243:42: error: unused
parameter 'input' [-Werror=unused-parameter]
  243 | Dump::visit (AttrInputMetaItemContainer &input)
      |              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~

* With those worked around (see below), there still a couple of
-Werror=dangling-reference
  errors:

/vol/gcc/src/hg/master/rust/gcc/rust/typecheck/rust-hir-type-check-type.cc: In
member function 'Rust::TyTy::BaseType*
Rust::Resolver::TypeCheckType::resolve_segments(Rust::NodeId, Rust::HirId,
std::vector<std::unique_ptr<Rust::HIR::TypePathSegment> >&, std::size_t,
Rust::TyTy::BaseType*, const Rust::Analysis::NodeMapping&, Location)':
/vol/gcc/src/hg/master/rust/gcc/rust/typecheck/rust-hir-type-check-type.cc:465:13:
error: possibly dangling reference to a temporary [-Werror=dangling-reference]
  465 |       auto &candidate = *candidates.begin ();
      |             ^~~~~~~~~
/vol/gcc/src/hg/master/rust/gcc/rust/typecheck/rust-hir-type-check-type.cc:465:44:
note: the temporary was destroyed at the end of the full expression
'candidates.std::set<Rust::Resolver::PathProbeCandidate>::begin().std::_Rb_tree_const_iterator<Rust::Resolver::PathProbeCandidate>::operator*()'
  465 |       auto &candidate = *candidates.begin ();
      |                    

I've hacked around both by adding -Wno-error=unused-parameter
-Wno-error=dangling-reference
to gcc/rust/Make-lang.in (RUST_CXXFLAGS), but this is supposed to work out of
the box. The build is in stage 2 now.

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Rainer Orth from comment #0)
> /vol/gcc/src/hg/master/rust/gcc/rust/typecheck/rust-hir-type-check-type.cc:
> In member function 'Rust::TyTy::BaseType*
> Rust::Resolver::TypeCheckType::resolve_segments(Rust::NodeId, Rust::HirId,
> std::vector<std::unique_ptr<Rust::HIR::TypePathSegment> >&, std::size_t,
> Rust::TyTy::BaseType*, const Rust::Analysis::NodeMapping&, Location)':
> /vol/gcc/src/hg/master/rust/gcc/rust/typecheck/rust-hir-type-check-type.cc:
> 465:13: error: possibly dangling reference to a temporary
> [-Werror=dangling-reference]
>   465 |       auto &candidate = *candidates.begin ();

This should probably be:

    auto first = candidates.begin ();
    auto &candidate = *first;

so that the iterator persists as long as its value is needed.

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Oh wait, that's a std::set::iterator? Then the warning is wrong. Its operator*
returns a reference to something that outlives the iterator itself.

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I thought this had been fixed by

commit 32a06ce38a38bf37db468f0e6c83520fcc221534
Author: Marek Polacek <polacek@redhat.com>
Date:   Tue Nov 1 17:05:52 2022 -0400

    c++: Quash -Wdangling-reference for member operator* [PR107488]

    -Wdangling-reference complains here:

      std::vector<int> v = ...;
      std::vector<int>::const_iterator it = v.begin();
      while (it != v.end()) {
        const int &r = *it++; // warning
      }

is the operator* here a non-member function?

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Actually, the patch I plan to post in a little bit should fix the problem above
because the reference we're initializing here is non-const.

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
https://gcc.gnu.org/pipermail/gcc-patches/2022-November/605800.html, if
accepted, should help.

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[ro at CeBiTec dot Uni-Bielefeld.DE]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

--- Comment #6 from ro at CeBiTec dot Uni-Bielefeld.DE <ro at CeBiTec dot Uni-Bielefeld.DE> ---
> --- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
> https://gcc.gnu.org/pipermail/gcc-patches/2022-November/605800.html, if
> accepted, should help.

The patch doesn't apply cleanly to the devel/rust/master branch,
unfortunately.  Even when I adjust it manually, the build fails with

/vol/gcc/src/hg/master/rust/gcc/cp/call.cc: In function 'void
maybe_warn_dangling_reference(const_tree, tree)':
/vol/gcc/src/hg/master/rust/gcc/cp/call.cc:13547:5: error: 'std_pair_ref_ref_p'
was not declared in this scope
13547 |  || std_pair_ref_ref_p (type)))
      |     ^~~~~~~~~~~~~~~~~~

I'll leave this to the rust developers to figure out: my primary goal
was to check if the branch still builds on Solaris and has reasonable
rust test results.

Another message to the developers is to try a bootstrap build once in a
while: while non-bootstrap is certainly reasonable during development,
finding that bootstrap is broken shortly before the merge date isn't the
best idea, I believe ;-)

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[dkm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

--- Comment #7 from Marc Poulhiès <dkm at gcc dot gnu.org> ---
Hello,

(I'm merely proxying some info here)

We do have regular bootstrap builds (see
https://builder.sourceware.org/buildbot/#/builders/107 ) and were aware of the
breakage (but I'm not sure you can observe it in this builder, I'll investigate
why)

Arthur already has a pending change that should fix this, see: 

 https://github.com/Rust-GCC/gccrs/pull/1635

Not really sure how it interacts with Marek's fix. I've pinged Arthur so this
will be handled at some point :)

Thanks!

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[cohenarthur.dev at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

Arthur Cohen <cohenarthur.dev at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |cohenarthur.dev at gmail dot com

--- Comment #8 from Arthur Cohen <cohenarthur.dev at gmail dot com> ---
Hi there,

The problem has been fixed and our bootstrap build is green again :) this will
be fixed in the v4 of patches that I will send soon.

Sorry for the frustration caused!

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #9 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed then.

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

Thomas Schwinge <tschwinge at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|i386-pc-solaris2.11         |
              Build|i386-pc-solaris2.11         |
               Host|i386-pc-solaris2.11         |
           Assignee|unassigned at gcc dot gnu.org      |tschwinge at gcc dot gnu.org
                 CC|                            |tschwinge at gcc dot gnu.org
           See Also|                            |https://github.com/Rust-GCC
                   |                            |/gccrs/pull/1703

--- Comment #10 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #3)
> I thought this had been fixed by
> 
> commit 32a06ce38a38bf37db468f0e6c83520fcc221534
> Author: Marek Polacek <polacek@redhat.com>
> Date:   Tue Nov 1 17:05:52 2022 -0400
> 
>     c++: Quash -Wdangling-reference for member operator* [PR107488]

ACK; <https://github.com/Rust-GCC/gccrs/pull/1703>.

[Bug rust/107633] [13 regression] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

Thomas Schwinge <tschwinge at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://github.com/Rust-GCC
                   |                            |/gccrs/pull/1701

--- Comment #11 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
(In reply to Rainer Orth from comment #0)
> hundreds of instances of -Werror=unused-parameter

For the record, these were "fixed" ;-) with
<https://github.com/Rust-GCC/gccrs/pull/1701> "Standardize warning flags".

[Bug rust/107633] Bootstrap failure due to -Werror=unused-parameter and -Werror=dangling-reference

[tschwinge at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107633

Thomas Schwinge <tschwinge at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |build
            Version|13.0                        |rust/master
            Summary|[13 regression] Bootstrap   |Bootstrap failure due to
                   |failure due to              |-Werror=unused-parameter
                   |-Werror=unused-parameter    |and
                   |and                         |-Werror=dangling-reference
                   |-Werror=dangling-reference  |

--- Comment #12 from Thomas Schwinge <tschwinge at gcc dot gnu.org> ---
(In reply to Marc Poulhiès from comment #7)
> Arthur already has a pending change that should fix this, see: 
> 
>  https://github.com/Rust-GCC/gccrs/pull/1635

... which has later been reverted; needs some more attention.

---

However, all issues reported here (as far as I understand) have now been
addressed individually in GCC/Rust master branch.  (At least,
x86_64-pc-linux-gnu bootstrap is now again "green" in my testing.)